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1O2                             PRIMITIVE   UNGULATA                             CHAP.
possess of earlier mammals, we rnust arrive at the general con-
clusion that two of the existing larger groups of the Eutherian,
non-Marsupial, mammals were differentiated at quite the begin-
ning of the Eocene., and were represented by forms from which
it is possible to derive at least the existing Carnivora, Insectivora,
Artiodactyla, and, Perissodactylu. These were the Creodonta and
the Ungulate Coiidylarthra. In addition to these we may
enumerate as very early types the Lemuroidea, represented by
such forms as Indrodon in the "New World, and (though later) by
Wecrolemur, etc., in the Old "World, and the Edentata, if we are
to allow as their ancestors the Ganodonta.
The early Eocene strata also contain representatives of at
least one order, the Amblypotla, which increased subsequently,
but has died out without descendants, unless we are to believe
with some that the Elephants are to be derived from these
Eocene ** pachyderms/1' In later Eocene times the great majority
of the existing orders, and even subdivisions of orders, are to be
met with ; and there are in addition such totally extinct orders
as the Typotheria, Aiicylopoda, and Tillodontia. Coupled with
this gradual specialisation in the orders of Eutherian mammals,
there is naturally a vast increase in the number of generic and
family types. This culminates perhaps in the Miocene, from
which time tliere has been a gradual decline in mammalian
variety, so that it is justly said that we live now in an epoch
which is impoverished of mammals. This gradual decay has
persisted until to-day, as is witnessed by the extinction of the
I&hytina and the Quagga, and the growing rarity of the White
Ilhinoceros and the American Bison.
The early Eutherian stock consisted of small mammals
with small heads and slender, long tails. The limbs were
pentadactyle, ensheathed in claws or broader hoofs. The fore-
limbs may have been partly prehensile. The teeth were forty-
four, completely differentiated into incisors, canines, molars, and
preniolars ; and there appears to have been a complete diphy-
odontism. The canines were nob greatly enlarged, and no
diastexna separated any of the teeth. The molars were bunodont
or of a more cutting pattern, with some five or six tubercles.
These animals were, moreover, very small-brained. This early
stock is represented by Creodoiit and Condylarthrous animals,
the exact boundaries between which are hardly marked in the